Fix alpha type when doing GPU color space conversion of unpremul images

Fixes fringing seen on bottom row of
https://gold.skia.org/detail?test=makecolorspace&digest=eccdd2a952d9503734b35b3a725a18b2

Change-Id: I4d05a2edab99dc989f4088d38a13827384f0444a
Reviewed-on: https://skia-review.googlesource.com/150121
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

Author: brianosman

src/image/SkImage_Gpu.cpp

@@ -970,9 +970,11 @@ sk_sp<SkImage> SkImage_Gpu::onMakeColorSpace(sk_sp<SkColorSpace> target, SkColor
         return nullptr;
     }
 
+    SkAlphaType newAlphaType = (kUnpremul_SkAlphaType == fAlphaType) ? kPremul_SkAlphaType
+                                                                     : fAlphaType;
     // MDB: this call is okay bc we know 'renderTargetContext' was exact
     return sk_make_sp<SkImage_Gpu>(fContext, kNeedNewImageUniqueID,
-                                   fAlphaType, renderTargetContext->asTextureProxyRef(),
+                                   newAlphaType, renderTargetContext->asTextureProxyRef(),
                                    std::move(target), fBudgeted);
 
 }